The present invention generally relates to systems, apparatus and/or methods for detecting physical characteristics of samples. More particularly, the invention relates to systems, apparatus and/or methods for detecting physical irregularities or imperfections in webs. Yet more particularly, the invention relates to systems for detecting physical irregularities or imperfections in recording tapes, for example, video tapes.
The assignee of the present invention, Research Technology, Inc., has been selling systems for detecting physical irregularities or imperfections in recording tapes, specifically video tapes. In these systems, a video tape is reviewed and evaluated for physical damage in the form of, for example, holes, creases, scratches, et cetera.
As a general rule, in such systems, light is directed onto a section of the tape and reflected light is received by one or more photocells which then generate signals containing information concerning the nature of the surface of the tape section under examination. In this regard, a tape surface ideally is smooth. Light reflected from the smooth surface generally will reflect at an angle equivalent to that of the incident light. However, if an irregularity such as a crease or a hole is present on the surface of the tape, then the light will reflect at a different angle.
If a photocell is positioned at the expected angle of reflection, a smooth surface will reflect the incident light evenly toward the photocell. However, a damaged surface will reflect the light unevenly such that the photocell will detect either an increase (bright spot) or decrease (shadow) in reflected light.
Although such prior art systems basically have worked well for their intended purpose, there is room for improvement. In particular, because a photocell is a discrete device, it is incapable of discriminating between portions of the surface of a tape, i.e. the resolution is low. Accordingly, information about the physical characteristic of the surface of the tape can only be generated for large defects.